Not sure what happened here, but I don't have any dated logs so this is in retrospect.
We laid a floor using standard floor boards over the laid joists. This gives a bit of insulation, but also the height to allow the various pipes and wires to run inside.
Before the floor could be put down, the gas and waste had to be put through, as well as conduit for wires. Connecting things together, fitting the gas isolation taps could now take place.
That big piece of black pipe in the picture is the balanced flue for the Truma combo heater. Thinking it would be hard to fit, I did the external part first to cut it to the correct length. It was still hard to fit in the confined space. Note to self, if doing this again, allow a lot more space.